Periodicity

Question 1

What is the covalent radius?

Answer 1

The distance from the centre of the nucleus to the outer edge of the atom

Question 2

What is the trend in covalent radius going across a period?

Answer 2

The covalent radius decreases because as you go across a period, there is an increase in the number of protons (and therefore nuclear charge) in each element which pulls the electrons closer to the nucleus, decreasing atomic size.

Question 3

What is the trend in covalent radius going down a group?

Answer 3

The covalent radius increases because as you go down a group, an extra shell of electrons is added to each element. The filled inner electrons then ‘shield’ or ‘screen’ the outer electrons from the attractive nucleus, pulling the electrons further away from the nucleus, increasing atomic size.

Question 4

What is the first ionisation energy?

Answer 4

The first ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms

Question 5

How would you write the first ionisation energy of Magnesium?

Answer 5

Mg(g) –> Mg+(g) + e-

Question 6

What is the second ionisation energy?

Answer 6

The second ionisation energy is the energy required to remove the next mole of electrons

Question 7

How would you write the second ionisation energy of Magnesium?

Answer 7

Mg+(g) –> Mg2+(g) + e-

Question 8

What is the trend in ionisation energy going across a period?

Answer 8

Ionisation energy increases because as you go across a period there is an increase in the number of protons (and therefore nuclear charge) in each element which pulls the electrons closer to the nucleus, making them harder to remove

Question 9

What is the trend in ionisation energy going down a group?

Answer 9

Ionisation energy decreases because as you go down a group, an extra shell of electrons is added to each element. The filled inner electrons then ‘shield’ or ‘screen’ the outer electrons from the attractive nucleus, decreasing the attraction between them, making them easier to remove.

Question 10

Why are the second ionisation energy values always bigger than the first?

Answer 10

Because when an electron has been removed, the number of protons will always be more than the number of electrons, making the nuclear attraction of the remaining electrons greater

Question 11

Why are ionisation energy values which involve an electron being removed from a full shell of electrons so high?

Answer 11

Because an electron is being removed from an electron shell which is closer to the nucleus

Question 12

How do you calculate the enthalpy change in:
Na(g) –> Na2+(g) + 2e-

Answer 12

Add the first and second ionisation energy values
(496 + 4562 = 5058kj mol l^-1)

Question 13

What is electronegativity?

Answer 13

A measure of the attraction an atom involved in a bond has for the electrons involved in that bond

Question 14

What is the trend in electronegativity going across a period?

Answer 14

Electronegativity increases because as you go across a period, there is an increase in the number of protons (and therefore nuclear charge) in each element which results in a greater attraction between the nucleus and the bonding electrons

Question 15

What is the trend in electronegativity going down a group?

Answer 15

1.Electronegativity decreases because with every shell of electrons added, the bonding electrons are further away from the nucleus. This increase in distance reduces the attraction between the nucleus and the bonding electrons.

2.The inner filled electrons also ‘screen’ the bonding electrons from the nucleus which reduces their attraction to the nucleus